As the decrease in size and the enhancement in performance of electronic equipment are required, integrated circuits (ICs) mounted on a printed wiring board 1 as shown in FIG. 1 have been evolving from package-type ICs 2 to bare IC chips 3 shown in FIG. 2, and further to multi-chip modules 5 as shown in FIG. 3.
In an arrangement shown in FIG. 2, bare IC chips 3 are mounted directly on a printed wiring board 1 by means of die bonding and wire bonding. The areas of the printed wiring board required for mounting the bare IC chips are smaller as compared with a case in which package-type ICs 2 covered with armoring material such as plastic or ceramics are mounted on the printing wiring board 1. However, if after mounting a lot of bare ICs chips 3 on a printed wiring board 1, any of the bare ICs chips 3 is found to be defective, the board 1 itself is scrapped because it is difficult and troublesome to remove the defective bare IC chip from the board 1 (to repair the board 1). In other words, there is a problem that the manufacturing process results in a poor yield.
A multi-chip module 5 which solves the above problem is shown in FIG. 3. Referring to FIG. 4 and 5, the manufacturing process of this multi-chip module 5 is briefly described. In the process, bare IC chips 52 are fixed by die bonding on a multilayer printed wiring board 51, and the electrical connections are achieved by wire bonding. Each bare IC chip is fit with a dam frame, and sealed with resin. Then, lead terminals 55 of the Gull Wing Type are soldered as outer electrodes to the electrode pads provided on the peripheral regions of the printed wiring board 51, thus completing the multi-chip module 5.
Since in case of multi-chip modules 5, each multi-chip module can be tested alone in the operation, only the multi-chip modules 5 which have been passed the test can be mounted on a printed wiring board such as a mother board (hereinafter, a printed wiring board on which multi-chip modules are to be mounted is referred to as a "target printed wiring board").
However, there are following problems in these conventional multi-chip modules. First, a lot of lead terminals 55 have to be soldered to the periphery of the printed wiring board 51. For this, the number of working processes increases, and the packaging density on a main printed wiring board 1 is reduced by the areas on the target printed wiring board 1 which are occupied by the lead terminals 55.
In the second place, the size of the printed wiring board 51 becomes larger as compared with the size of bare IC chips mounted on the printed wiring board 51 because a circuit pattern (not shown) for electrically interconnecting a plurality of bare IC chips 52 has to be provided around the bare IC chips 52.
In the third place, in such an arrangement that each bare IC chip 52 is fit with a dam frame 53 for sealing with resin 57, large areas are occupied by the dam frames 53 so attached as to enclose the respective bare IC chips 52. This also causes the size of the printed wiring board 51 to become large.
Also, the dam frames 53 are glued to the printed wiring board 51 by inserting projections 53a provided on each dam frame 53 into holes 51a of the printed wiring board 51 for positioning. Accordingly, the printed wiring board 51 is provided with a lot of positioning holes 51a, which make the circuit pattern complicated and cause the size of the printed wiring board 51 to become large.
Further, if sections of a multi-chip module 5 which have been enclosed by dam frames 53 are to be absorbed by a vacuum absorber 7 in mounting the multi-chip module 5 on a main printed wiring board 1, enough absorption area can not be obtained because of the small size of each dam frame 53. Thus, the absorbing and holding of multi-chip module is difficult, and operations tend to be unstable.
In the fourth place, if resistors and capacitors for adjusting the circuit are provided for a multi-chip module to form a compound module, then around the bare IC chips 52 there have to be extra areas where chip resistor elements, chip capacitor elements and electrode pads to which they are soldered are disposed. This also cause the size of the printed wiring board 51 to become large. And, since the chip elements have to be soldered after sealing the bare IC chips with resin, the number of working processes increase.
On the other hand, if the chip resistor and capacitor elements are mounted on the printed wiring board on which the multi-chip module 5 is mounted, the area for mounting the module 5 including the chip elements increases, causing the size of the target printed wiring board to become large.
As described above, in conventional multi-chip module: the number of attaching processes of the lead terminals; the size becomes larger in accordance with the number of the lead terminals; the printed wiring board increases in size because of a circuit pattern for interconnecting the bare IC chips; the number of processes of attaching dam frames to the bare IC chips; the attaching of dam frames causes the size of the printed wiring board; it is difficult to vacuum-absorbing dam frame sections for mounting the multi-chip module to the main printed wiring board.
There is also another problem that if resistors and capacitors for adjusting the circuit are provided for a multi-chip module to form a compound module, then the size of the multi-chip module becomes large, thereby increasing the size of the printed wiring board on which the multi-chip module is mounted.
The present invention is intended for solving these and other problems and disadvantages of the prior art. An object of the invention is to providing a multi-chip module which can be made smaller than a conventional one, which can be manufactured in a reduced number of process, and which can be easily mounted to a main printed wiring board by means of vacuum absorption.